This invention relates to a method of controlling heat input to a waste heat boiler operated in conjunction with a coke dry quenching station, and more particularly, to such a method and apparatus wherein heat input to the waste heat boiler is maintained substantially constant and substantially independent of the amount of hot coke dumped into the station, by utilizing the sensible heat of bleeder gas exiting from the top of the station.
Hot coke taken from an oven is now quenched in a dry quenching system, such as depicted in FIG. 1. The prior system comprises a quenching station 1, wherein a vertical cooling chamber 2 is formed, and is connected to an external boiler 3 in which waste heat contained in the heat quenching gas from the quenching station 1 is used to produce steam and to be concurrently cooled and supplied again through recirculating passages 7, A and blower 4 to station 1 for quenching another charge of hot coke. The furnace 1 usually has a bleeder mechanism 12. Usually boiler 3 has coils 10 which contains heat exchanging medium such as water to cool the quenching gas coming from the furnace 1 after quenching hot coke, and by heat exchange the medium is turned into steam, for example, which is then utilized by utilization apparatus 11. In such a system, quenching gas if sent into the furnace 1 from an inlet located toward the bottom thereof by blower 4. Then, the gas is passed through the layers of hot coke dumped into the cooling chamber of the furnace and is heated by the sensible heat of the hot coke. Concurrently, the coke itself is cooled. Then, the heated quenching gas is drawn off from the upper portion of the cooling chamber and is conducted to the boiler 3 wherein the heat contained in the quenching gas causes the water in coil 10 to become steam and the quenching gas is cooled by heat exchanger action. The cooled heat exchanged quenching gas is then recirculated by blower 4 into chamber 2 via passage "A".
The waste heat boiler used in connection with the dry quenching system for coke, produces steam for power generation and other general plant uses, and cools the quenching gas, which cooled quenching gas is then recirculated to quench the hot coke. Provided the steam output is reliable and constant, this dual usage can be very profitable in terms of savings of energy and resources. Accordingly, smooth, reliable, and constant operation of the waste heat boiler is an important consideration, especially now in times of escalating energy costs. However, the present situation in the art is that it is very difficult to maintain constant the amount of steam produced by the waste heat boiler because of the difficulties in controlling the amount of heat taken from the quenching station, which heat depends to an extent upon the amount of coke supplied to the quenching chamber and the pushing interval of the charges of coke.
The amount of steam produced by the boiler is dependent upon the heat supplied to it by the heated quenching gas drawn from the quenching station after quenching. This heat input is related to the amount of hot coke dumped into the quenching station. Consequently, the number of calories of the heated quenching gas decreases as the dumped amount of hot coke decreases. Thus, the heat input to the boiler is lowered.
In the art, the following counter-measure has been taken to resolve the problem. The heat input to the boiler is controlled by adjusting the dumping interval into the quenching furnace and keeping the hot coke in the cooling chamber filled to a constant level. It is, however, well known that the pushing interval of hot coke taken from an oven is not always constant and the pushing schedule is often changed by various factors. Accordingly, when the pushing interval changes, the heat input to the boiler directly undergoes a change, and thus the amount of steam produced is lowered. It is thus unavoidable that such a reduction of steam brings about dropping of load for the generator and its power generation becomes unstable and unreliable. Thus, the problem of maintaining constant heat input to the waste heat boiler, and maintaining constant steam output, has still not been resolved in a satisfactory manner.